U.S. patent application number 14/568323 was filed with the patent office on 2016-06-16 for method of predicing injection molding cycle time.
The applicant listed for this patent is The Procter & Gamble Company. Invention is credited to Sean Wang.
Application Number | 20160167295 14/568323 |
Document ID | / |
Family ID | 56110289 |
Filed Date | 2016-06-16 |
United States Patent
Application |
20160167295 |
Kind Code |
A1 |
Wang; Sean |
June 16, 2016 |
METHOD OF PREDICING INJECTION MOLDING CYCLE TIME
Abstract
The invention features, in general, a method for determining a
target cycle time for an injection molded part. The method
comprises the steps of ascertaining the solidified volume
percentage (V.sub.n) as a function of cooling time (T.sub.n) data
for solidification of an injection molded part and calculating a
cooling speed indicator (CSI.sub.n) for each data point,
(T.sub.n,V.sub.n). The solidified volume percentage (V.sub.n) as a
function of cooling time (T.sub.n) and solidified volume percentage
(V.sub.n) as a function of cooling speed indicator (CSI.sub.n) are
tabulated and used to determine a target cycle time.
Inventors: |
Wang; Sean; (Boston,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Procter & Gamble Company |
Cincinnati |
OH |
US |
|
|
Family ID: |
56110289 |
Appl. No.: |
14/568323 |
Filed: |
December 12, 2014 |
Current U.S.
Class: |
264/40.1 |
Current CPC
Class: |
G06F 30/20 20200101;
B29C 2945/76892 20130101; B29C 45/00 20130101; B29C 2945/76561
20130101; G06F 2113/22 20200101; B29C 2945/76558 20130101 |
International
Class: |
B29C 65/00 20060101
B29C065/00 |
Claims
1. A method of determining a target cycle time for injection
molding a production part, comprising the steps of: a. creating a
computer based model of an injection molded part; b. creating a
computer based model of a mold for an injection molded part; c.
ascertaining the solidified volume percentage (V.sub.n) as a
function of cooling time (T.sub.n) data for solidification of the
injection molded part from V.sub.0=0% to V.sub.total=100%; d.
calculating a cooling speed indicator (CSI.sub.n) for each
solidified volume percentage as a function of time data point
(T.sub.n,V.sub.n); e. determining the solidified volume percentage
(V.sub.n) as a function of a cooling speed indicator (CSI.sub.n)
data, (CSI.sub.n,V.sub.n), from V.sub.0=0% to V.sub.total=100%; f.
determining a Turning Point (CSI.sub.n,V.sub.n).sub.Turning Point
for solidified volume percentage (V.sub.n) as a function of a
cooling speed indicator (CSI.sub.n) data; g. determining a target
cycle time (T.sub.n) corresponding to the solidified volume
percentage (V.sub.n) at the Turning Point; and h. applying the
target cycle time to the production molded part.
2. The method according to claim 1 wherein CSI n = ( Tn - Tn - 1 )
/ Ttotal Vn - Vn - 1 / Vtotal . ##EQU00006##
3. The method according to claim 2 wherein the Turning Point,
(CSI.sub.n,V.sub.n).sub.Turning Point, is a data point,
(CSI.sub.n,V.sub.n), having a minimum value defined by ( CSIn ) 2 +
( 100 - Vn ) 2 2 . ##EQU00007##
4. The method according to claim 2 further comprising the step of:
a. producing a first graph of solidified volume percentage
(V.sub.n) as a function of cooling time (T.sub.n).
5. The method according to claim 4 further comprising the step of:
a. producing a second graph of the solidified volume percentage
(V.sub.n) as a function of a cooling speed indicator
(CSI.sub.n).
6. The method according to claim 5 further comprising the step of:
a. determining a Turning Point on the second graph for solidified
volume percentage (V.sub.n) and a cooling speed indicator
(CSI.sub.n).
7. The method according to claim 6 further comprising the step of:
a. determining a target cycle time by finding the cycle time
(T.sub.n) on the first graph corresponding to the solidified volume
percentage (V.sub.n) at the Turning Point on the second graph.
8. The method according to claim 6 wherein the Turning Point
(V.sub.n, CSI.sub.n).sub.Turning Point is the point having a
minimum distance to a data point defined by solidified volume
percentage (V.sub.n)=(V.sub.total)=100% and CSI.sub.n=CSI.sub.0=0
wherein distance = ( CSIn ) 2 + ( 100 - Vn ) 2 2 . ##EQU00008##
9. A method of determining a target cycle time for injection
molding a production part, comprising the steps of: a. creating a
computer based model of an injection molded part; b. creating a
computer based model of a mold for an injection molded part; c.
ascertaining the solidified volume percentage (V.sub.n) as a
function of cooling time (T.sub.n) data for solidification of an
injection molded part from V.sub.0=0% to V.sub.total=100%; d.
calculating a cooling speed indicator (CSI.sub.n) for each
solidified volume percentage as a function of time data point
(T.sub.n,V.sub.n), where CSI n = ( Tn - Tn - 1 ) / Ttotal Vn - Vn -
1 / Vtotal ; ##EQU00009## e. determining the solidified volume
percentage (V) as a function of a cooling speed indicator (CSI)
data, (CSI,V) from V.sub.0=0% to V.sub.total=100% ; f. determining
a Turning Point (CSI.sub.n,VO.sub.Turning Point for solidified
volume percentage (V.sub.n) as a function of a cooling speed
indicator (CSI) data, wherein the Turning Point,
(CSI.sub.n,V.sub.n).sub.Turning Point, is a data point,
(CSI.sub.n,V.sub.n), having a minimum value defined by ( CSIn ) 2 +
( 100 - Vn ) 2 2 ; ##EQU00010## g. determining a target cycle time
(TO corresponding to the solidified volume percentage (V.sub.n) at
the Turning Point; and h. applying the target cycle time to the
production molded part.
10. The method according to claim 9 further comprising the step of:
a. producing a first graph of solidified volume percentage
(V.sub.n) as a function of cooling time (T.sub.n).
11. The method according to claim 10 further comprising the step
of: a. producing a second graph of the solidified volume percentage
(V.sub.n) as a function of a cooling speed indicator
(CSI.sub.n).
12. The method according to claim 11 further comprising the step
of: a. determining a Turning Point on the second graph for
solidified volume percentage (V.sub.n) and a cooling speed
indicator (CSI.sub.n) wherein the Turning Point (V.sub.n,
CSI.sub.n).sub.Turning Point is the point having a minimum distance
to a data point defined by solidified volume percentage
(V.sub.n)=(V.sub.total)=100% and CSI.sub.n=CSI.sub.0=0 wherein
distance= = ( CSIn ) 2 + ( 100 - Vn ) 2 2 . ##EQU00011##
13. The method according to claim 12 further comprising the step
of: a. determining a target cycle time by finding the cycle time
(T.sub.n) on the first graph corresponding to the solidified volume
percentage (V.sub.n) at the Turning Point on the second graph.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to cycle time for injection
molding. Particularly, a method of predicting optimal injection
molding cycle time is provided.
BACKGROUND OF THE INVENTION
[0002] Injection molding of parts made of thermoplastic material
generally has three main phases: first, injection of material into
a mold; second, packing and cooling of the material in the mold in
forming the desired part, and third, ejection of the molded part
from the mold. The molding cycle time is commonly referred to as
the duration of time from the start of the injection phase to
initiation of the ejection phase.
[0003] Ability to accurately predict molding cycle time is of
paramount importance in injection molding, particularly since it
relates directly to the production rate and part quality. When
cycle time exceeds a desired range, the production rate is
compromised. In some instances, the part may exhibit brittle
failure during ejection due to excessively increased friction
force. In addition, ejector pins can be damaged due to the friction
force exceeding the maximum ejection force that can be withstood by
the ejectors. Further, if the part is ejected prematurely when only
a thin layer of polymer is solidified, ejection may cause permanent
deformation leading to surface defects. For most injection molders,
cycle time is estimated through molding trials which are costly and
time consuming. It is even more difficult to determine a proper
cycle time range for new materials due to lack of knowledge of the
material behavior.
[0004] Production tooling for the injection molding process is very
costly to build. Capital cost is linearly proportional to the cycle
time; therefore, cycle time minimization is critical in product
cost reduction. Modeling software can be used to optimize the
molding process in the early design phase. Modeling software
calculates temperatures, velocities, viscosities, shear rates, and
pressures as a function of time. However, the cycle time prediction
is still left for users to predict.
[0005] Consequently, a need exists for an innovation which will
provide an effective approach to predicting an injection molding
target cycle time that can be used to determine an optimal cycle
time for an injection molded part.
SUMMARY OF THE INVENTION
[0006] The invention features, in general, a method for optimizing
cycle time for an injection molded part. The method comprises the
steps of ascertaining the solidified volume percentage (V.sub.n) as
a function of cooling time (T.sub.n) data from V.sub.0=0% to
Vtotal=100% for solidification of an injection molded part and
calculating a cooling speed indicator (CSIn) for each data point,
(T.sub.n,V.sub.n), where
CSI n = ( Tn - Tn - 1 ) / Ttotal Vn - Vn - 1 / Vtotal .
##EQU00001##
The solidified volume percentage (V.sub.n) as a function of cooling
time (T.sub.n) and solidified volume percentage (V.sub.n) as a
function of cooling speed indicator (CSI.sub.n) are tabulated from
(0.0) to (?,100%) and a Turning Point is determined. The Turning
Point is the data. point, (CSI.sub.n,V.sub.n).sub.Turning Point,
having a minimum value defined by
( CSIn ) 2 + ( 100 - Vn ) 2 2 . ##EQU00002##
From the tabulated data, the cycle time (T.sub.n) corresponding to
the solidified volume percentage (V.sub.n) at the Turning Point is
the target cycle time (T.sub.n).sub.Target for the injection molded
part. The target cycle time is used to determine the optimal cycle
time for the injection molded part.
[0007] Alternatively, the method of optimizing cycle time for an
injection molded part, further comprises the steps of using the
solidified volume percentage (V.sub.n) as a function of cooling
time (T.sub.n) data to produce a first graph of solidified volume
percentage (V.sub.n) as a function of cooling time (T.sub.n) and
using solidified volume percentage (V.sub.n) as a function of
cooling speed indicator (CSI.sub.n) data to produce a second graph
of the solidified volume percentage (V.sub.n) as a function of
cooling speed indicator (CSI.sub.n). A Turning Point is determined
on the second graph which is a data point defined by a solidified
volume percentage (V.sub.n) and a cooling speed indicator
(CSI.sub.n) having a minimum distance to a data point defined by
solidified volume percentage (V.sub.n)=(Vtotal)=100% and
CSI=CSI.sub.0=0 wherein
distance = ( CSIn ) 2 + ( 100 - Vn ) 2 2 . ##EQU00003##
The target cycle time is determined by finding the cycle time on
the first graph corresponding to the solidified volume percentage
(V.sub.n) at the Turning Point on the second graph.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter which is
regarded as forming the present invention, it is believed that the
invention will be better understood from the following description
taken in conjunction with the accompanying drawings.
[0009] FIG. 1 is a graph of percent solidification versus cooling
time of injection molded handle 1.
[0010] FIG. 2 is a graph of percent solidification versus cooling
speed indicator for injection molded handle 1 identifying the
turning point.
[0011] FIG. 3 is the graph of percent solidification versus cooling
time of injection molded handle 1 shown in FIG. 1 identifying the
target cycle time corresponding to the percent solidification at
the turning point found in the graph in FIG. 2.
[0012] FIG. 4 is a graph of percent solidification versus cooling
time of injection molded handle 2.
[0013] FIG. 5 is a graph of percent solidification versus cooling
speed indicator for injection molded handle 2 identifying the
turning point.
[0014] FIG. 6 is the graph of percent solidification versus cooling
time of injection molded handle 2 shown in FIG. 4 identifying the
target cycle time corresponding to the percent solidification at
the turning point found in the graph in FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present disclosure includes methods of simulating
injection molding of injection molded parts. Embodiments of the
present disclosure can at least assist in predicting a target cycle
time for the injection molded part. As a result, the cycle time of
the injection molded part can be optimized.
[0016] Computer aided engineering (CAE) is a broad area of applied
science in which technologists use software to develop computer
based models of real world things. The models can be used to
provide various information about the physical behavior of those
real world things under certain conditions and/or over particular
periods of time. With CAE, the interactions of the computer based
models are referred to as simulations. Sometimes the real world
things are referred to as a problem and the computer based model is
referred to as a solution.
[0017] There are several major categories of CAE. Finite element
analysis (FEA) is a major category of CAE, in which models of
mechanical components and/or assemblies are used to predict stress,
strain and other mechanical behaviors. Computation fluid dynamics
(CFD) is another major CAE category, in which models of fluids
(e.g. liquids and/or gases) are used to predict pressure, flow,
temperature, and other fluid and/or thermal properties. Still
another major category of CAE is fluid structure interaction (FSI),
which models the physical behavior of fluids in relation to solid
objects. There are also a number of other categories of CAE.
[0018] Some aspects of CAE can also relate to various Computer
Aided technologies, sometimes collectively referred to as CAx. CAx
includes a number of technologies, such as Computer Aided Design
(CAD), Computer Aided Manufacturing (CAM), and Knowledge Based
Engineering (KBE).
[0019] Commercially available software can be used to conduct CAE.
Abaqus, from SIMULIA in Providence, R.I., and LSDyna from Livermore
Software Technology Corp. in Livermore, Calif., are examples of
commercially available FEA software. Fluent, from ANSYS, Inc. in
Canonsburg, Pa., and Flow3D, from Flow Science, Inc. in Santa Fe,
N. Mex. are examples of commercially available CED software. LSDyna
is also an example of FSI software. CAE software can be run on
various computer hardware, such as a personal computer, a
minicomputer, a cluster of computers, a mainframe, a supercomputer,
or any other kind of machine on which program instructions can
execute to perform CAE.
[0020] CAE software can be applied to a number of real world
things, such as injection molded parts. SIGMASoft is a CAE software
that can be used to optimize the molding process in the early
design phase of an injection molding process. SIGMASOFT considers
the thermo and fluid properties of the injection molded part and
calculates temperatures, velocities, viscosities, shear rates,
pressures, etc. as a function of time. However, the cycle time
prediction of the injection molded part is still left for users to
interpret. By leveraging SIGMASOFT's output a method was developed
and applied to predict the cycle time for injection molded plastic
parts. The method has been found to provide an estimation of cycle
time, and also identify where to focus in order to reduce cycle
time for an injection molded part.
[0021] An injection molded razor handle was used to find a
practical way of predicting cooling time. However, any number of
injection molded parts could be used. The production cooling time
was compared to the cooling time predicted by the injection molding
software SIGMASOFT revealing that the solidification starts off
very quickly and slows down dramatically as it approaches the 100%
solidification.
[0022] The graph shown in FIG. 1 shows the solidified volume
percentage (V.sub.n) as a function of cooling time (T.sub.n) data
from V.sub.0=0% to V.sub.total=100% for solidification of the
injection molded razor handle (handle 1). As evidenced from the
graph, a Turning Point exists where the solidification slows down
significantly. The Turning Point can be used to determine the
target cycle time for the injection molded part.
[0023] The solidification rate for an injection molded part can be
determined by the relation dv/dT. It has been determined that the
inverse of the solidification rate can be used to calculate a
relationship referred to as cooling speed indicator (CSI.sub.n).
Cooling speed indicator, (CSI.sub.n), is a dimensionless parameter
that can be calculated for each data point, (T.sub.n,V.sub.n),
where
CSI n = ( Tn - Tn - 1 ) / Ttotal Vn - Vn - 1 / Vtotal ( 1 )
##EQU00004##
From the relationship for Cooling Speed Indicator in Equation (1),
when CSI.sub.nequals 1, a "balanced" solidification process exists
where solidifying 1% of the volume requires 1% of the total
solidification time. When this value is smaller than 1 the
solidification is fast since it takes less than 1% of the total
time to solidify 1% of the volume. When it is larger than 1, the
solidification is slow, taking more than 1% of the total time to
solidify 1% of the volume. By plotting the solidified volume
percentage as a function of CSI a curve is produced where the
Turning Point used to determine the target cycle time for the
injection molded part becomes more apparent as evidenced from the
plot shown in FIG. 2.
[0024] The Turning Point is the mid-point of the corner of the
curve in FIG. 2. The actual Turning Point is the point
(CSI.sub.n,V.sub.n) closest to the point (0,100). From the
solidified volume percentage (V.sub.n) as a function of cooling
speed indicator (CSI.sub.n) data from (0,0) to (?,100%) the actual
Turning Point, (CSI.sub.n,V.sub.n).sub.Turning Point, is determined
as the minimum distance defined by
Distance = ( CSIn ) 2 + ( 100 - Vn ) 2 2 . ( 2 ) ##EQU00005##
[0025] From the data, the cycle time (T.sub.n) corresponding to the
solidified volume percentage (V.sub.n) at the Turning Point is the
target cycle time (T.sub.n) for the injection molded part. The
target cycle time is used to determine the optimal cycle time for
the injection molded part.
[0026] Once the minimum distance is determined using Equation (2)
to identify the Turning Point (CSI.sub.n,V.sub.n).sub.Turning
Point, the target cycle time corresponding to the data point
(CSI.sub.n,V.sub.n).sub.Turning Pointcan be determined from the
data tabulated in Table I below or using the plot in FIG. 1. The
cycle time corresponding to the solidified volume percentage at the
Turning Point (CSI.sub.n,V.sub.n).sub.Turning Point in FIG. 2 is
located on the curve in FIG. 1. The plot in FIG. 3 illustrates how
the plot in FIG. 1 of Solidified volume vs. Cooling Time is used to
determine the target cycle time by drawing a vertical line through
the point on the curve where the solidified volume percentage
(V.sub.n) corresponds to the solidified volume percentage
(V.sub.n).sub.Turning Point at the Turning Point
(CSI.sub.n,V.sub.n).sub.Turning Point in FIG. 2.
TABLE-US-00001 TABLE I Time Melt (Seconds) CSI Volume % Distance 0
0.17837 5.4 94.60017 0.25 0.13259 11.24 88.76010 0.58 0.24849 21.61
78.39039 1.14 0.30417 31 69.00067 1.87 0.37704 41 59.00120 2.85
0.40440 51.83 48.17170 3.74 0.41667 61 39.00223 4.79 0.56519 71.5
28.50560 6.08 0.90343 81.01 19.01148 7.24 1.24046 86.36 13.69629
8.8 1.60088 91.6 8.55119 9.53 2.03869 93.5 6.81221 10.9* 4.16667
96.3 5.57235 11.8 8.59375 97.2 9.03839 13.45 14.79167 98 14.92627
17 29.16667 99 29.18380 24 100 0.00000
[0027] The data provided in Table I reveals a target cycle time of
10.9 seconds for handle 1 which was determined to be close to the
actual production cooling time of 12.0 seconds. It is interesting
to note that subsequent to the target cycle time, it actually takes
an additional 12 seconds to solidify the last 3% of the melt
volume. This is because a solidified shell has been developed on
the outside of the handle, and the heat exchange between the
plastic material and the steel mold becomes less efficient. In
addition, it takes longer distance for the heat to transfer from
the center of the handle to the outside surface. For this reason,
it was found that it was not necessary to achieve 100%
solidification prior to removing the injection molded handle from
the mold.
[0028] This learning was applied to a second handle, handle 2.
Handle 2's solidification history graph is shown in FIG. 4. The
target cycle time can be identified using FIG. 5 which shows the
turning point corresponding to 97.2% solidification at a Cooling
Speed Indicator of 3.6. From FIG. 6, the target cycle time
corresponding to 97.2% solidification is 18 seconds. The target
cycle time was determined to be close to the actual production
cycle time of 18.5 seconds.
[0029] Regarding all numerical ranges disclosed herein, it should
be understood that every maximum numerical limitation given
throughout this specification includes every lower numerical
limitation, as if such lower numerical limitations were expressly
written herein. In addition, every minimum numerical limitation
given throughout this specification will include every higher
numerical limitation, as if such higher numerical limitations were
expressly written herein. Further, every numerical range given
throughout this specification will include every narrower numerical
range that falls within such broader numerical range and will also
encompass each individual number within the numerical range, as if
such narrower numerical ranges and individual numbers were all
expressly written herein.
[0030] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0031] Every document cited herein, including any cross referenced
or related patent or application is hereby incorporated herein by
reference in its entirety unless expressly excluded or otherwise
limited. The citation of any document is not an admission that it
is prior art with respect to any invention disclosed or claimed
herein or that it alone, or in any combination with any other
reference or references, teaches, suggests or discloses any such
invention. Further, to the extent that any meaning or definition of
a term in this document conflicts with any meaning or definition of
the same term in a document incorporated by reference, the meaning
or definition assigned to that term in this document shall
govern.
[0032] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *